A judge in the Netherlands has opened the door to a potential avalanche of legal cases against Shell over environmental degradation said to be caused by its oil operations in the Niger Delta.

The oil group expressed "disappointment" tonight that a court in The Hague had agreed to allow Friends of the Earth Netherlands and four local Nigerian farmers to bring a compensation case in its backyard for the first time.

Environmental campaigners insisted the case in the Netherlands was only being brought as a final resort and they declined to put a figure on the kind of damages stemming from the test case involving four farmers and alleged pollution at Oruma in Bayelsa state. But they said a variety of independent organisations in the past had estimated that the wider oil industry may be responsible for up to $20bn (£12.5bn) worth of damage as a result of pipeline spills and flaring of gas.

Geert Ritsema, a spokesman for the Dutch environmentalist group, said: "For years, these people have been trying to get Shell to clean up its mess and stop polluting their habitat. However, again and again they have come away empty-handed.

"That is why they are now trying to get justice in the Netherlands. The court decision is an initial victory for all Nigerians that have been fighting for years for a cleaner habitat and justice," he added.

Friends of the Earth claims the oil spills are not accidents but represent a pattern of systematic pollution and contempt for the rights of the local population that had been going on for decades, something denied by the oil group.

Up until now compensation claims have been brought in Nigeria, but many have become bogged down in a congested court system.

Alai Efanga, one of the plaintiffs in the Oruma case, said: "Our village was pleased with the [initial] decision of the Dutch court. We hope that Shell will now quickly clean up the oil pollution so that we can resume growing food and fishing."

The three other plaintiffs are all farmers and fishermen from the villages of Oruma, Goi and Ikot Ada Udo, all located in the oil-rich Niger Delta, which is one of Shell's most important oil-producing areas. The substantive hearing of the first lawsuit is expected to be held in the spring of 2010 but Shell said it continued to believe that the case should not be heard in the Netherlands.

A Shell spokesman said: "It is with disappointment that we learned of the district court ruling. We believe there are good arguments on the basis of which the district court could have concluded that it lacks jurisdiction in respect of SPDC [Shell Petroleum Development Corporation] in these purely Nigerian matters."

Friends of the Earth Netherlands said an important hurdle had been overcome paving the way for an appropriate court hearing. But oil industry sources said that Shell was being unfairly targeted, given that the oil spill had been caused in the first place by sabotage.

Last June, the oil group agreed to pay $15.5m in settlement of a legal action in which it was accused of having collaborated in the execution of the writer Ken Saro-Wiwa and eight other leaders of the Ogoni tribe of southern Nigeria.